Theoretical neutron-capture cross sections for r-process nucleosynthesis in the ${}^{48}$Ca region

Abstract

We calculate neutron capture cross sections for r-process nucleosynthesis in the ${}^{48}$Ca region, namely for the isotopes ${}^{40-44}$S, ${}^{46-50}$Ar, ${}^{56-66}$Ti, ${}^{62-68}$Cr, and ${}^{72-76}$Fe. While previously only cross sections resulting from the compound nucleus reaction mechanism (Hauser-Feshbach) have been considered, we recalculate not only that contribution to the cross section but also include direct capture on even-even nuclei. The level schemes, which are of utmost importance in the direct capture calculations, are taken from quasi-particle states obtained with a folded-Yukawa potential and Lipkin-Nogami pairing. Most recent deformation values derived from experimental data on $\beta$-decay half lives are used where available. Due to the consideration of direct capture, the capture rates are enhanced and the "turning points" in the r-process path are shifted to slightly higher mass numbers. We also discuss the sensitivity of the direct capture cross sections on the assumed deformation.

Comments: 6 pages; talk at ENAM95, appeared in the proceedings, uploaded here to allow easy access. in Proc. Int. Conf. on Exotic Nuclei and Atomic Masses "ENAM 95", eds. M. de Saint Simon and O. Sorlin (Editions Frontières, Gif-sur-Yvette 1995), p. 683